Project Summary (30 lines) Stuttering is a highly variable condition: People exhibit different amounts of stuttering behavior in different tasks, when talking to different people, in different settings, and at different times. Although variability is widely acknowledged, most assessments of stuttering behavior, whether conducted in a clinical setting or for research, involve brief speech samples collected in a small number of settings that do not reflect natural communication (e.g., monologuing or reading aloud). Unfortunately, we do not know if these clinic/laboratory measures are representative of people's speaking experiences in the real world. Ample evidence suggests that they are not, but the vast majority of clinical work and research on stuttering still does not account for this variability. This raises questions about the validity of existing research that relies on measures that may not be reflective of people's true stuttering behavior. In this project, we seek to overcome these uncertainties about the validity of stuttering measurement. We will collect the largest-ever samples of the everyday speech of people who stutter through continuous recording of conversational interactions over a 7-day period. This will allow us to examine the full range of stuttering behaviors that people exhibit across situations and over time. For Aim 1, we will use these unprecedentedly large speech samples to test whether current practices of collecting brief speech samples in clinical or laboratory settings are adequate. Pilot data and prior studies suggests that a broader range of measures will be needed in order to better reflect people's true stuttering behaviors. For Aim 2, we will develop a measurement model for stuttering using latent variable modeling to support new methods for evaluating stuttering that are more reflective of real-world variability. For Aim 3, we will use structural regression modeling to explore the ways in which key personal characteristics, such as the ways in which a person responds to stuttering, contribute to the experience of variability. For Aim 4, we will conduct a mixed-methods study to explore how variability affects the adverse impact that stuttering has on people's lives, with the ultimate goal of improving the assessment of stuttering so that we can reduce adverse impact and enhance quality of life for people who stutter. Overall Impact: Our findings will increase our understanding of the factors that contribute to the variability of stuttering and provide needed guidance for improving assessment of stuttering in clinical and laboratory settings. We will make our carefully transcribed, annotated speech samples available through FluencyBank, so that other researchers can use our data to answer many unanswered questions about stuttering in the real world. Our work has the potential to disrupt current thinking about stuttering measurement while simultaneously providing a solution about how researchers and clinicians can better assess stuttering to gather more representative measures of people's fluency in their daily lives.